- Boilers
- Gas boiler
F64
Vaillant F.64 on a gas boiler: electronics or sensor fault
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Vaillant F.64 means a fault in the electronics, a safety sensor or its cable. If you smell gas or fumes, get out and follow the warnings. If not, take a photo of the code and call an authorised professional.
Safety first
Stop and check this first
- If you smell fumes indoors: Vaillant says to open doors and windows fully, switch the appliance off and call an authorised professional. A badly monitored flame or poor combustion can fill the home with carbon monoxide, which has no smell: if you feel headache, dizziness or nausea, ventilate, get out and call for help. A CO alarm helps.
- If you smell gas: do not operate switches, sockets, doorbells or phones, no flames or smoking, open doors and windows, close the meter valve and the appliance gas valve if you can, warn neighbours without using the bell, leave the building and call the gas company from outside. That is what Vaillant asks.
Safe checks you can perform
- Smell of gas or fumes
- Code steady or coming and going
- Sensor, flame and electronics check by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Flow sensor and cable measurement
- Do not attempt this professional task: Ionisation current
- Do not attempt this professional task: Combustion analysis after the repair
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Flow sensor and cable measurement
What they doThe technician measures the flow sensor resistance and the continuity of its cable and connector.
They must show youthe resistance measured against the manufacturer's table.
In writingthe value and any part replaced.
Ionisation current
What they doMeasures the ionisation electrode signal with the burner running and checks the electrode and its cable.
They must show youthe current measured against the manufacturer's specification.
In writingthe condition of the electrode and what was replaced.
Combustion analysis after the repair
What they doWith the boiler running, connects an analyser to the flue gas test point and checks combustion.
They must show youthe CO2 and CO measured against the manufacturer's table.
In writingthe values measured.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Smell of gas or fumes
- Who:
- you.
- How:
- without any flame nearby, notice whether there is a smell of gas or fumes near the boiler.
- Result that matters:
- whether there is any smell.
- If it smells of gas:
- follow Vaillant's gas warning and leave the home.
- If it smells of fumes:
- open doors and windows, switch the appliance off and call an authorised professional.
- Evidence to keep:
- a note of the time and what you noticed.
Evidence: Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
Code steady or coming and going
- Who:
- you.
- How:
- take a photo of the display and note whether F.64 shows all the time or only now and then, and when. Vaillant says to call an authorised professional when an F.xx message appears.
- Result that matters:
- whether the fault is continuous or intermittent.
- If it is continuous:
- call the authorised professional.
- If it comes and goes:
- tell the technician; a loose contact in a cable fits better than a broken part.
- Evidence to keep:
- photos of the code with date and time.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01 · Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
Sensor, flame and electronics check by the technician
- Who:
- authorised professional.
- How:
- checks the flow sensor and its cable, measures the ionisation electrode signal for instability and checks the electronics, as Vaillant's table says.
- Result that matters:
- which part is giving the wrong signal.
- If the sensor or cable is at fault:
- it is repaired or replaced.
- If the flame signal is unstable:
- the electrode and its circuit are checked.
- Evidence to keep:
- a report of what was measured and replaced.
Vaillant reserves inspection, maintenance, repair and gas adjustments to an authorised professional: the user does not open the boiler. The electrode and burner are gas and combustion parts.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01 · Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Vaillant
- Product type
- Gas boiler
Known code variants
- ecoTEC plus F.64
- Error F64 Vaillant
- F.64
- Vaillant F.64
What it means
In the ecoTEC plus VMW table, F.64 is electronics/sensor fault and the cause is faulty electronics, safety sensor or cable. Vaillant says to check the flow sensor, the cable to that sensor, the flame detection sensor, for example the ionisation electrode, for an unstable signal, and the electronics. The boiler uses these signals to control the burner safely. The code does not say which of the four parts has failed.
Warnings and stop conditions
- Higheditorial warning
If you smell fumes indoors: Vaillant says to open doors and windows fully, switch the appliance off and call an authorised professional. A badly monitored flame or poor combustion can fill the home with carbon monoxide, which has no smell: if you feel headache, dizziness or nausea, ventilate, get out and call for help. A CO alarm helps.
Evidence: Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
- Criticalsource verified
If you smell gas: do not operate switches, sockets, doorbells or phones, no flames or smoking, open doors and windows, close the meter valve and the appliance gas valve if you can, warn neighbours without using the bell, leave the building and call the gas company from outside. That is what Vaillant asks.
Evidence: Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
Symptoms and causes
Probable causes · in order
- Faulty flow sensorPossible
Vaillant lists it first for F.64. If the flow sensor reads wrongly, the electronics cannot monitor temperature. The technician measures it against the manufacturer's table.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01
- Sensor cable or connectionPossible
A damaged cable or loose contact to the sensor cuts the signal. It fits if the code comes and goes or after work inside the boiler.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01
- Unstable flame signalPossible
The flame detection sensor, such as the ionisation electrode, can give an unstable signal. It can only be checked by measuring the ionisation current.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01
- Faulty electronicsLess common
If sensors and cables are fine, the circuit board remains. It is the last option after checking everything else.
Evidence: Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01
Virtual technician
Does F64 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Vaillant ecoTEC plus VMW ..6/5-5, instrucciones de instalación y mantenimiento 0020244991_01
Vaillant · 2017 · manual
- 2
Vaillant ecoTEC plus VM, VMW y VMI ..6/5-5, instrucciones de funcionamiento 0020243851_02
Vaillant · 2017 · manual
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